For biological reasons, it is desirable to employ together the two systemic fungicides 1,1'-piperazine-1,4-diyldi-[N-(2,2,2-trichloroethyl)-formamide] and methylbenzimidazole-2-ylcarbamate, also known as triforine and carbendazim, respectively, for control of fungal diseases in plants. Preparations containing both active substances are desired to facilitate better handling of the active substance combinations.
Triforine develops its full activity only if it is used in dissolved form. To obtain good stability of triforine concentrates, they are formulated with addition of salts of dodecyclbenzene sulfonic acid (DBS), in particular, amine salts. Carbendazim is preferably used in the form of wettable powders.
In accordance with the prior art, the problem of producing a combined liquid formulation of the active substances sufficient for practical requirements seemed to be unsolvable. Triforine is sufficiently soluble only in very few solvents. In these solvents, however, the solubility of carbendazim is too low, between 0.7 percent and 0.35 percent at room temperature, to produce solution concentrates. On the other hand, this solubility is too high for assuming that carbendazim solid substance might be processed to a sufficiently stable suspension in these solvents. When such preparations are stored, or shelved, crystal growth due to the Ostwald-ripening would be expected, according to the present level of knowledge. Such crystal growth would make the preparations unfit for use as fungicidal agents.
Carbendazim itself forms soluble DBS salts. Employment of the DBS salt, which salts are, according to German Offenlegungsschrift No. 25 21 284, important for the stability of triforine preparations, increases solubility of the carbendazim. This reduces the chance of impeding the growth of crystals. Also, carbendazim cannot be used directly in form of the soluble DBS salts of carbendazim (German Offenlegungsschrift No. 24 17 008), as these salts are unstable, hydrolyze within a short time, and lead to non-reversible precipitation of carbendazim in large crystals.
In addition, the carbendazim adducts disclosed in German Offenlegungsschrift No. 22 19 174 are unstable in the mixtures with triforine and DBS salts. Furthermore, liquid preparations of carbendazim are disclosed in German Offenlegungsschrift Nos. 19 57 712, 21 54 020, 23 03 757, and 23 54 467 and in Japanese patent application No. 72 40 060. However, these liquid preparations cannot be considered for use in fungicidal compositions with triforine since, for example, metal salts catalyze decomposition of triforine and triforine is insoluble in mineral oils and cannot exhibit fungicidal activity.